Television apparatus



May 31, 1938.

H. M. LEWIS ET AL TELEVISION APPARATUS Filed Oct. 8, 1934 7 Sheets-Sheet 1 INVENTORS ATTORNEYS May 31, 1938. H. M. LEWIS ET AL TELEVISION APPARATUS '7 Sheets-Sheei 2 Filed 001;. 8, 1934 U lNyENToRs Y f/MZEW/53 M [an/e02 pwyw hw ATTO R N EYS May 31, 1938. H. M; LEWIS ET AL TELEVISION APPARATUS Filed Oct. 8, 1934 '7 Sheets-Sheet 3 INVENTORS ATTORNEY5 y 3 I H. M. LEWIS ET AL 2,118,977

TELEVISION APPARATUS Filed Oct. 8, 1934 7 Sheets-Sheet 5 INVENTORS H M10445 M (awe/r2 ,L 6) ,(D K iL -M ATTORNEYS May 31, 1938, I H. M. LEWIS El AL I 7 TELEVISION APPARATUS Filed Oct. 8 1934 7 Sheets-Sheet e INVENTORS v I Ail/1 eW/s 5 M. Can em BY I.

ATTORNEYS May 31, 1938.

H. M. LEWIS ET AL TELEVISION APPARATUS Filed 001;. 8, 1934 7 Shegts-Sheet 7 ATTORN EY5 i Patented May 31,1938

uni-rap STATES PATEN OFFICE 'rsmvrsiou APPARATUS Harold M. Lewis. Douglaston. Long Island. and

Madison Gawain. Manhas set. N. Y.. assignors to Haseltine Corporation. a corporation lie!- was... 0mm 8. m4. sens: No. 141.324

8 Claims. (01. 250-27) 1 10 A primary object of the invention is to produce voltage oi saw-tooth wave form to serve as an electrostatic control of scanning in a cathode ray television receiver. Another primary object of this invention is to produce current of saw-tooth 15 wave form through inductance toprovide the new. for magnetic control of scanning in a cathode ray television receiver. Another. object of this invention is to provide circuitsand apparatus {or generating the saw-tooth andrelated wave forms go in a precisely controllable and economical manner for use in television. Another object of the invention is to generate voltage and current wave forms related to the saw-tooth wave forms which will serve to govern or control'the generation oi voltage or current of saw-tooth form.

These and other objects of the invention will be clear from the specification which iollows particularly as it relates to the description of the drawings in which:

Figs. la-ld inclusive, illustrate as applied to a cathode-ray tube. the manner in which voltages and currents of saw-tooth and related wave forms are employed to eflect scanning in a television receiver.

Fig. 2 is a schematic diagram of a cathode-ray television receiver to illustrate the essential units required for receiving, scanning and controlling a television image- Figs. lid-3e inclusive, graphically depict a soealled derivative series of wave forms of which the saw-tooth form is one, to illustrate the voltage and current relationships relative to pure reactances, such as inductance and capacity shown diagrammatically in Figs. 3) and 39 respectively. Figs. 4a, b and c, are graphs explanatory of the fcorrect use of the saw-tooth wave forms in scanning the lines in a television picture.

Figs. 511-5] inclusive. are graphs similar to those of Fig. 4. illustrative of the use of the saw- 50 tooth wave form for scanning at picture frequency.

Figs. Git-6g inclusive, are a series oi. fundamental circuits pertaining to the generation of voltages and currents oi saw-tooth and related 55 wave forms.

Figs. 7a and b and Figs. 8a and b, are diagrams of the wave forms of current and voltage resulting from operation of certain of the Figs. 8a.- to So circuits. an Figs. 9a, b and c, and Figs. 10a, b and c, are

graphs illustrating the use oi combined sawtooth and impulse wave iorm for scanning in television.

Figs. 11c. b and c, are graphs illustrating wave form suitable for causing current of saw-tooth wave form to flow in an impedance.

Fig. 12 is to a simple form oi inductance in series with resistance type or generator, designated as the L/R type.

. 'Flgs. 13c. b and 0. show vacuum tube arrangements for utilizing impulse, or impulse plus sawtooth voltage wave forms to cause a saw-tooth wave form .0! current to flow through inductance,

Fig.--14 shows a resistance-capacity or R. C type of generator operating as 'an impulse voltage source ior a scanning inductance. Fig. 15 shows a-similar resistance capacity typ oi generator-arranged to function as an impulse generator ior causing saw-tooth waveform of current-toilew through an inductance.

Figisid is a simplified circuit developed from Fi Figs. 17, 18, 19a and 19b represent strictly L/R type generators oi saw-tooth currents; I

Figs. 20, 21 and 22 show the use of resistancecapacity type generators as properly poled sources oi saw-tooth plus impulse voltage for grid control of vacuum tubes whereby saw-tooth current is caused to flow through inductance in the tube output circuits.

Fig. 23 is a vacuum tube arrangement simulat ing the fundamental L/R circuit 0! Fig. 16.

Fig. 24 illustrates the use of a dynatron as an L/R. generator 01' saw-tooth current through an inductance.

The present application is one of a series oi related copending applications to the same inventors, which in aggregate, describe a complete television transmitting and receiving system employing saw-tooth and related wave forms for line and picture scanning. In copending application oi' H; M. Lewis. Serial No. 747,070, flied October 5, 1934, there is described the trans-- copendingapplications, or its equivalent. is to be received to provide the vision irequency signals and control impulses referred to in this application ior reproducing the image at the receiver.

The present application thereiore, is restricted to just so much of the descriptions oithe copeiiil ing applications as is requisite to an understanding of the novel aspects of this application.

In the several drawings, elements which perform the same function in each case, are similarly labeled; those of a fundamental nature being labeled by letters. Otherelements are labeled numerically.

Referring to Fig. 1, A represents the luminescent-screen end of a cathode-ray tube K, upon which the scanning traces are indicated as they would appear in their ideal form when no signal is being received and, applied to modulate the grid of tube K to control the intensity of the electron beam striking the screen. This ideal trace is of saw-tooth wave form in that each line is a linear trace from left to right (indicated by heavy line m to represent a constant value of illumination of the screen) and a rapid (practically zero time) retrace-from right to left (indicated bya light line 12) since practically no electrons strike the screen in this brief retrace interval and the illumination is therefore weak. Similarly,- the succession or rate at which the lines are traced is shown to be linear with time from top to bottom of the screen since the lines m and n are evenly spaced for the lines shown and the retract p. q from bottom to top of. the picture is shown to be rapid in that it occurs in the time required for two lines to be traced; and hence these two lines appear oppositely sloped in the picture retrace. Thus, in the example illustrated the line frequency 111., n saw-tooth wave form has an almost infinite ratio between time of trace and retrace, and the picture frequency p, q, saw-tooth wave form has a ratio of trace to retrace shown as 10 to 1.- This manner of scanning the picture from left to right and from top to bottom is termed rectilinear scanning.

At the present time, for a television picture of reasonable quality, the number of pictures trans mitted per second may be taken as 24, and the line frequency taken as 2880 per second. At least this is a sufllcient definition of quality to serve in this application for purposes of describing the inventions. r

The ratio of picture trace to retrace time is in practice about 40 to 1 (much better than shown in the illustration). Hence, with the line frequency of 2880 per second, there are 117 lines in each picture and three lost in the picture retrace. This ratio has a correspondence dimensionally to the ratio between the height of picture in a standard mm. motion picture film and the opaque space separating adjacent picture frames (the film to space ratio being, in fact, about 30 to 1). Hence to scan motion picture film as described in the mentioned copending application Serial No. 747,070, only the time re-. quired for three or four lines can be lost in the retrace without losing a part of thev picture height. trace-to-retrace ratio in practice is about 10 to 1 which. is far from the ideal of zero time shown in Fig. 1.

To cause the cathode ray to scan the screen it may be deflected by magnetic or electro-static fields. Magnetic deflection is illustrated in Fig. 1. The coils L1, L1 serve to provide the field for the picture frequency scanning while L2, L2 similarly serve to provide the field for line frequency scanning. Since the magnetic field changes proportionally to the current flowing in these coils, the current through L1, L1 must have As for the line frequency, a reaso-nable tooth wave form at the line frequency m, 11 rate. 4

such as 2880 per second. In order readily tounderstand the nature of the voltage required to cause such a current in j the scanning coils, and to arrive at other voltage and current relationships which may be desired. a series of wave forms related to the sawtooth' wave form has been plotted and is shown in Figs. 3a to Be inclusive. This may be termed a derivative series", since any of the wave forms shown is the mathematical derivative of the wave form immediately below it in the series. The utility of this series as it stands relates to pure reactance, since fundamentally the volt age er. across an inductance, Fig. 3f, is the derivative of the current 11. through the inductance, and the current in through a condenser, Fig. 3g, is the derivative of the voltage 80 across the condenser; Hence using the notation at the left of the figure, if a current through a pure inductance has any of the wave forms shown, the voltage acrossthe inductance must be of the wave form shown immediately above, and if a voltage across a pure condenser has any of the wave forms shown the current through the condenser is of the wave form shown immediately above in the series. Fig. 3c is the desired wave form for scanning and is shown as providing a ratio of 10 to 1 in the time of trace to retrace. Fig. 3:: will be referred to as a double-impulse; Fig. 3b as an impulse; Fig. 3c as a saw-tooth, and Fig. 3d as a parabolic impulse wave form.- The form Fig. 3e

requires cubical equations to represent it mathematically.

In Fig. 1a, the current in coils L1, L1, and that in coils L2, L2 is labeled in to indicate its wave form as being that ofv Fig. 3c and the voltages applied in both cases are necessarily of impulse wave form and hence labeled 83b to indicate the wave form as being that of Fig. 3b. I

In Fig. 1b the cathode ray tube K employs deflecting plates for electrostatic scanning, wherein P1, P1 are the deflecting plates for the'picture frequency and P2, P2 the deflecting plates for the line frequency scanning. Since the deflection of the electron stream is proportional to the voltage between the deflecting plates, the voltage across P1, P1 should be saw-tooth as indicated by the notation 63c and that across plates P2, P: similarly should be saw-tooth in form as labeled 83c.

Fig 1c illustratesmagnetic deflection. coils L1, for the picture frequency'and electrostatic deflection, plates P2,. for the line frequency, and hence the voltage required to cause'saw-tooth current in L1, L1 is of impulse wave form 83b as indicated,

and the voltage across plates P2, P2 is of sawv tooth form 83c.

The saw-tooth wave is also important in mechanical systems of scanning, which do not use" rotating elements but which, nevertheless, must accomplish rectilinear. scanning. For example,

if a light valve is to be employed to vary the light.

intensity in accordance with the picture detail and the light is then to be scanned to spread a this figure the cathode dry tube is the source of light as well as the light valve, having in its simplestform a cathode I, a control grid 2, an

control the number of electrons which pass I through 8 and hence produce light in proportion to their number on striking the fluorescent screen A. No special elements have been indicated here or in the preceding representations of the tube to control the focus of the ray striking the screen, since such focus may be controlled by electrostatic or magnetic fields as best serves the construction of the particular tube employed. Lens 5 serves to focus the spot of light from A on screen 8 via the mirror surfaces of oscillographtype vibrator mirrors 8 and I which determine the path of the light. It will be clear from the description of Fig. 10 that vibrator 8 must act to deflect the light on the screen according to a sawtooth form at the line frequency and similarly vibrator I must cause the light to traverse the screen linearly from top to bottom and rapidly back to the top in saw-tooth form at the picture frequency. The angle through which the mirror surfaces turn and hence the motion of light on the screen is assumed to be directly proportional to the current through the vibrators and to the voltage applied; hence in each case, the actuating voltage required is; as indicated, of the form Fig. 80.

To better understand the specific circuits which follow, it is desirable first to consider broadly the functioning of the receiver and the cooperation of its parts, whereby the scanning operation at the receiver is synchronized with the transmitter and the picture correctly reproduces. Hence in Fig. 2 a diagram of the receiver is shown wherein unit blocks serve to indicate broadly the functions of the various receiver parts. The receiver illustrated is of the superheterodyne type -in that the incoming carrier wave and sidebands are collected by antenna structure 9, amplified by the ratio frequency amplifier l0, and applied to modulator II, together with heterodyne energy from oscillator [2, to produce an intermediate frequency carrier and sidebandswhich are amplified by the intermediate frequency amplifier i3 and applied to detector M. The detector M develops the vision frequencies, which represent detail in the picture. and also line and picture frequency impulses, which are to serve-for synchronizing the scanning at the receiver with that at the transmitter during each line retrace and each picture retrace interval. In order that the picture appearing on the screen shall be a "positive and the impulse modulation of the carrier shall function for "block-cu of retraces, the proper poling of the output from 3 is applied to vision frequency amplifier l5 and the proper poling of the output of i5 as applied to the cathode ray tube grid 23 must be observed, so that as the cathode ray 06 traces its pattern on the screen 25, the trace lines will be light or dark in accord with the corresponding line being traced at the transmitter. and the retrace lines will be black.

To make the case general, the cathode ray tube 70 is shown as having magnetic control cells L1, Li.

' for the picture frequency and electrostatic control plates P2, Pa, for the line frequency as was the casein Fig. 1c. The generator unit l8 serves to generate and supply saw-tooth voltage (labeled 7 83a) of line frequency to the deflecting plates Pa,

time intervals being shown as 10:1).

and to "block out" illumination of the screen Pa and the generator unit It here serves to causesaw-tooth current (in) to flow in deflecting coils L1, L1 (i. e.. it furnishes impulse voltage of form 83b across these coils).

To control the frequency and timing (phase) of the outputs of units It and II, the line frequency impulses and picture frequency impulses developed by detector ll are also applied to filter units (8 and I9. Unit I8 is. for example, a lowpass filter suitable for passing the picture frequency impulse undistorted in wave form to unit 20 which is the picture impulse amplifier and which serves to apply the picture impulse prop-'- erly poled and in adjusted amplitude as a control or synchronizing voltage to 2|. Similarly, unit i8 is, for example. a band-pass filter to pass the line impulse to amplifier II which in turn serves to apply the line impulses properly poled and adjusted in amplitude as a control or synchronizing voltage to it.

The arrows in the lines connecting units i8. i1 and i8, and similarly units I9, 20, 2|, indicate that these are one-way circuits and that no voltage from units it and 24 is to pass in the opposite direction so that these generators in themselves shall not affect each other nor shall they react back on the detector l4 and hence on the amplifier i5 and the cathode ray tube grid 23.

The wave form of the synchronizing impulse's supplied by M to units It and I8 is similar to that shown in Fig. 8b so that this graph may be taken as the form of impulse from It applied to control generator it. Thus, as shown in Fig. 4a, during the time interval t, u a line 111 is being traced on the screen, and during the interval u, t the retrace 11 occurs (the ratio of Similarly in Fig. 8b the control impulse endures for an interval v, w and is repeated after the trace interval w, v. This ratio of intervals is also shown as 10:1. Hence, if the impulse peak at 11, occurs simultaneously with the end of the trace it in Fig. 4a. perfect synchronism is assured.

Remembering new that the impulse, Fig. 8b, is applied to the cathode ray tube grid 23 poled negative to cause the screen to darken simultaneously with its application to unit It for control, it will be evident that the screen will be dark during the retrace and bright during the trace as shown in Fig. 4b. If, however, generator I8 is producing a saw-tooth voltage as in Fig. 4c in which the ratio of trace to retrace is, say 7 to 3 as shown, and if synchronismis secured inthat the points it of this voltage and v of the control impulse occur simultaneously, the

result is that shown in Fig. 40 where the retrace is blocked out as long as the synchronizing impulse interval 1:, w endures. Here, however, the transmitters li'ne trace starts at w which is prior to the cathode ray beam having reached the left edge of the picture so that in effect the left side of the picture is "folded under". Other relations giving improper synchronism will be seen to be possible depending upon the relative phase of the synchronizing impulses and the relative ratios of trace to retrace timebetween the transmitters scanning and the receiver's scanning processes. Hence for synchronism it is important in order that no part of the transmitted picture be lost, that the trace to retrace ratio of units 58 and 2| be as large or larger than that of the transmitted picture,

and that the scannings correspond in phase in orderthat each' line of the cathode ray tube screen starts with'the corresponding line of the transmitted picture and that the retr ces correspond so that retraces will be blocked o t as shown in Fig. 4b. v

Ifflgenerator l8 produces a voltage only :pproximating the required voltage 83c theni is important that the trace m part of theoycle should be linear but the shape oi retrace n is unimportant so long as its time interval is held sufliciently short. Non-linearity in the line traces would result in the traces (m in Fig.4) being curved and the picture detail would appear crowded together in some places and too widely spaced in others. The illustration is more easily given when non-linearity exists in the picture trace, as shown in Figs. 5a to 51 inclusive. Thus in Fig. 5a. the wave-form shown for the picture frequency is that of Fig. 3c and the proper uniform spacing of the picture lines which results are shown in the first corresponding pattern Fig. 5b. The second pattern Fig. 50 indicates how the retraces are absent when proper synchronization of the picture frequency is achieved and "block-out occurs.

Fig. 5d indicates that the saw-tooth current from generator II is of exponential form in both trace and retrace and the subsequent crowding of the lines at the bottom of the picture is shown in pattern Fig. 5e. With correct synchronization the retrace lines are blocked out as shown in pattern Fig. 5/.

It will be clear then that rigid requirements of design are imposed on generator units l8 and M of Fig. 2, in that they must supply saw-tooth voltage or current as the case requires having good. linearity in the trace, adequate ratio of trace to retrace time, and proper response to synchronizing'control voltages. Furthermore, the units l6 and H for the line control and I9 and for the picture control must fulfill two functions: (a) apply the synchronizing impulse undistorted and in proper amplitude and phase to units i8 and 2|. to effect synchronism; and (b) prevent reactions between these units and the rest of the system.

In the circuits which follow, fundamental circuits are first illustrated and specific circuits which perform the fundamental functions in a preferred manner are then given. It will appear that the units i6, ll, i9 and 20, Fig.2, may be dispensed with, in part or in whole, where the design of the units i8 and 2| is such as to render their assistance unnecessary.

In Figs. 6a. to Go, a number of fundamental circuits are shown for producing current and voltage wave forms related to the saw-tooth derivative series. The circuits of Figs. 6a, b and 0 will be termed the R, C, type in that the desired wave form results from the charge and discharge of a condenser through resistance. The circuits of Figs. 6d, e, j, and g. are termed the L/R type in that the wave form results from the flow of ,current through an inductance as affected by resistance.

In the modification of Fig. 6a, a pendulum S periodically short circuits 9. capacity (I through resistance r"'for a brief interval of time during each swing to the left, owing to closure of switch a. S is assumed to be actuated by some mechanism, as for example the usual clock eseapement, so that the frequency of recurring short circuits is here determined by S. For the values which 1 follow, the voltage across C relative to ground and the current-through C are to a close approximation as shown in Figs. 7a and 7b," respectively. E=300, volts, R=0.1 niegoh'm, r '=,5 0 0O ohms.

c=o.ooa ,ir.-, 'muo-or trace toretrace=b- =1 :1'.=

.f =22 cycles per second. v

During each interval that the contacts of switch .W are open, the condenser C is exponentially charged from source E throughlresistance R at a rate determined'by thetime constant of the circuit which depends'on the,produ'ct ofaR and C. During the 'retrace, that is,while"the contacts 'of switch a are closed by swinging of the pendulum to the left, the condenser C discharges through the resistance r at a ratedeplending upon the product oi. 1' and 'C. The effect of the path through R on the rate of discharge condenser C cancbe neglected since R is large. compared with r. The current through C, Fig. 7b. is the mathematical derivative of the voltage, Fig. 7a. It will be noted that the exponential saw-tooth voltage of Fig. 7a approximates the ideal form, Fig. 3c,

and that the exponential impulse, Fig. 7b,"ap-" proximates the ideal form, Fig. 3b.

The analogous case for an inductance is given in Fig. 6d, and the constants oi the circuits, listed below, may be so chosen that the same curves of Fig. 7 represent the resulting wave forms; Fig.

7a in this case being the current through the inductance L and Fig. 7b being the voltage across the inductance. In the circuit of Fig. 6b, the battery E supplies current through 1'. L and 0 during the trace part of the cycle. The pendulum is here labeled 0 to indicate that it is an "opening" device instead of the shorting device! of Fig. 4a. The contact to O is closed except during a brief interval during the end of the. swing of O to the right. The circuit constants mentioned to satisfy Fig. 7, are

The current throughL increases slowly and exponentially during the trace part of the cycle according to the time constant L/r. During the retrace the current falls rapidly and exponentially according to the timeconstant L/R. It will be noted that during the retrace the part of the circuit which includes E and r can be neglected (i. e., considered as of zero resistance) since R is large compared with r. this assumption is very small. The voltage across the coil is in this case the mathematical derivative of the currentthrough the inductance and is as shown in Fig. 7b.

In the R, C case Fig. 611, if circuit conditions permit values of R and C to be chosen sothat operation occurs over-only a small part of the exponential curve for thetrace then the trace will be sufllciently linear to serve as a saw-tooth wave form for scanning.

Similarly, if L and r in Fig. 6b are chosenso that operation occurs over only a-small-pfartof the exponential trace (1. e., L/r is large) the resulting current wave form may be acceptable for scan ning in television. f

The 'exponentiality of retrace in both cases is unimportant but the time of the retrace interval is quite important. The frequency in each case is determined by the periodicity ofthe pendulum, and the ratio of trace to retrace is obviously de- The error in making termined by the ratio of the time that the contact to the pendulum is closed to the time it is open.

In Fig. 6b, the same elements of the R, C type circuit are present with the exception that S in this case is a shorting device which acts to short circuit C through r when the voltage across has reached a predetermined maximum value. Assuming that the device S when closed (conductive) has no resistance and has infinite resistance when open (non-conductive) the same wave forms of voltage and current as shown by Fig. 7 result here if all circuit constants are the same as in Fig. 6a and if the device 8 closes when the value of voltage across C reaches a maximum of 150 volts, (1. e., when conversely the voltage between ground and point X has fallen to 150 volts) and opens when the voltage across C has fallen to 50 volts. A typical relaxation" oscillator is this circuit in which is a gaseous discharge tube such as a Thyratron".

In practice the operating voltages of S may be controlled and when once they are fixed the fundamental frequency of the circuit can be readily set by adjusting either C or R, or both. Also, 1' airects frequency as shown by the equation for the generated frequency given below.

1 (1) V E V 1 2 C(R log -I-r log Where: I =frequency in cycles per second C =capacitance in farads V1=maximum i-n volts developed across R. Vz=minimum in volts developed across E =maximum available battery voltage.

For a given adjustment Of 'S the amplitude of saw-tooth voltage developed across C is independent of frequency.

In the analogous L/R type of circuit, Fig. 6e,

the device 0 is substituted for the. pendulum of 0 of Fig. 6d and is assumed to be a device normally closed or conductive and of zero resistance when closed, until the current through it reaches a predetermined maximum value at wh ch instant it opens to become non-conductive. If the conditions are prescribed that O is conductive for all currents less than 30 milliamperes but non-conductive for currents exceeding this value. then with the remaining circuit constants as given for Fig. 6d, the wave forms of Fig. '7 again apply: Fig. 7a representing the current through L and Fig. 7b the voltage across L. In practice, if the adjustment of 0 remains unchanged, the frequency can be controlled primarily by changing r or L, or both. The equation for frequency is as given below, and again for a fixed condition of O, the frequency can be varied without changingthe amplitude or output current through L.

rR 7T1 1 z L r log -i-R log I II) flows In part, many of the circuits which follow relate to apparatus and arrangements which serve as the device 8 in R, C type circuits and as the device 0 in the LIE. type circuits. Furthermore,

synchronization is generally effected in connec-' v tion with the controlling of S or O as the case may be, as will appear later. For the present,

however, attention is directed to those parts of the circuits which control the trace of the cycle. Thus in Fig. 6c the'device H replaces R of the preceding R. C circuits, and in the simple form illustrated is a two-element vacuum tube having the cathode temperatureadiusted (adjustment not shown) to give limited electron emission, so that current through the tube is the same throughout a wide range of voltage across it.-

The tube is therefore a constant current device and the charging of C through .H during the trace of the saw-tooth voltage cycle is therefore linear with time as desired. For the circuit constants given below, the voltage across H (which is also that across C alone plus a direct current component) is as shown in Fig. 8a and the current through C is as shown in Fig. 8b which is the mathematical derivative of Fig. 8a.;

ing its time interval is sumciently brief. The frequency is:

peres and other symbols have same significance as in Formulas l and 2.

Since the current through H is a constant steady value of direct current, and by Kirchoifs law, the sum of the currents flowing to the point X must be zero, the wave form of current through S is identical with that through C with the addition of a direct current component. The voltage across aresistor inserted anywhere in this loop (as for example the voltage across 1') will be of an impulse wave form, Fig. 8b. This circuit is therefore a source of current or voltages of sawtooth or impulse wave form or of a combination of 'he two.

Since the condenser C passes no direct current it is immaterial as to whether. its lower terminal is connected at point 11 as shown or whether this terminal is connected to ground G or to some intermediate point on the battery E. The action is entirely the same as to the current through C and the alternating voltage across it; a change in only the direct current voltage component across C results. Actually the curve, Fig. 8a,

is the voltage between X-and G and is obviously the voltage across C plus E or simply the voltage across H. I

An advantage of returning C to the plus terminal of. E results when the voltage source E has appreciable resistance since then E is located'in the constant current branch of the circuit and no impulse current flows through it. Hence any reaction through the power supply source is avoided in practical circuit arrangements. When Where: i=constant current through H in ami I returned to point .6 it is more correct to say that C is rapidly charged when S operates and that C discharges at a constant current rate through H. There is no'reversal, however, of the saw-tooth voltage generated.

In the R, C type circuit .Iust described a constant-current deyice served to linearize the voltage, trace. In an analogous manner a constant voltage device will serve to linearize the current trace in the L/R type generator. Thus in Fig. 6e the trace is exponential due to the fact that as the current increases through L, it likewise increases through 1' and thevoltage drop across 1' prevents the voltage across L remaining constant during the trace. If Fig. 3c is the current through L then the voltage across L as shown by Fig. 3!) must be constant during the linear trace. Clearly if 2' were zero ,(and 1 includes any resistance present in the inductance L) then the voltage across L would remain'constant during the current trace when 0 is closed. Under such conditionsoFig. 8a represents the current through L and Fig. 8b the voltage across L for the constants which follow:

Where: E=.constant voltage in series with L, and

other symbols have same significance as in the preceding" formulas.

To make 1' zero a negative resistance -r may be introduced as is illustrated in Fig. 6).

The equivalent of introducing a negative resistance r to maintain constant the voltage across L during the trace is shown in Fig. 69 where a generator (330 of saw-tooth voltage properly poled and adjusted in amplitude is introduced in series with r and L. If the resultant current through L is of saw-tooth wave form then the voltage drop across 1' will be of saw-tooth wave form, and hence the insertion of generator 630 will compensate for the voltage drop across r to maintainthe voltage across L constant during the trace. Fig. 8a represents the current through L and Fig. 8b the voltage across L for this figure. Also the voltage across 0 is of impulse form since the sum of the voltage drops across 1', L, R and 33c must add up to the constant direct current voltage E.

The L/R circuit may be developed as an amplifier of an R, C generators output to produce saw-toothcurrent through scanning inductances.

.Or it may be developed as a self-sustaining genunderstood to be voltages, are shown first sep-.

arately and then combined to give a resultant saw-tooth plus impulse voltage wave form. Such circuit is indicated as L and R in series.

plates of the'cath'ode ray tube for picture irequency spanning. (with a saw-tooth form of control simultaneously operating for the line scanning) the pattern on the screen will be as shown in Fig. 9b. If the transmitters retrace endures for a time interval only one-half as long as that of the impulse component of this scanning wave, the picture retrace block-out will appear as shown in Fig. This blocks out that part of the picture retrace which lies across the field to be viewed and throws that part of the retrace which was not blocked out .above the field of view. These lines showing above the field of view constitute, of course, the top lines of -the picture which now must be'sacrificed and may be obscured by an .opaque mat (frame) .which will present only the field of view to theobserver. In effect, however, the retrace time has been shortened. i

In practice, it is generally more difficult to obtain a relatively sort retrace time in the case of high frequencies such as the line frequency.

' Hence by employing the combined saw-tooth and impulse for the line frequency voltage (this illustration being for the case of electrostatic scan-- ning) the folded under-part of the lines (as t,-w in Fig. 4a can bethrown to the left of the picture, and while this adds nothing of value to the left side of the image it does avoid the disturbing effect of the folded-under lines giving a'ghost. picture.

4 A proper proportioning of the relative amplitude of the two forms to be combined is important for correct results.

A perfect saw-tooth wave form having zero retrace time involves frequencies extending to infinity in the harmonic composition of the wave and it would be impossible to provide circuits for their use. U It can, however, be shownthat the plot of the summation of the first ten harmonics of the infinite Fourier series required to represent a saw-tooth wave having a 10:1 ratio of trace to retrace, Fig. 3c, is a curve very closely approximating the ideal. the plot of the summation of the first ten har- Similarly, it can be shown that A monies of the-infinite Fourier series required to represent a saw-tooth wave having zero retrace time does not, in comparison give a close approximation of its ideal.

Nevertheless, while recognizing this limitation,

"it is, at times, easier to generate a saw-tooth wave 'with a retrace interval which is too great and then improve this retrace time. The combination of an impulse and a saw-tooth having an exponential retrace (of form as in Fig. 8a) is given in Fig. 10. Here the resultant wave form is a, perfect saw-tooth with zero retrace time. The form of impulse which is here used to combine with the Fig. 8a form is not that of Fig. 8b but can be derived, to a close approxima- -tion, from Fig. 822 by rectification.

An equally important need for the combined saw-tooth and impulse wave form is required when the inductance, through which saw-tooth current is to flow, has resistance in series with it which is nearly always the case. This is shown for the ideal case in Fig. 11w, where the load The current is to be of the form of Fig. 3c and hence the voltage en is indicated as of that form. The voltage ex. is accordingly of the form of Fig. 3b as illustrated, and the resultant voltage which must be applied across this load is the wave form e shown. The resultant voltage e is here obtained by arbitrarily adding the instantaneous values ofthese two forms. Since the resultant wave form of e depends on the relative values of L and R, a second showing of the resultant wave form labeled e is indicated in which the impulse voltage across L is taken as one-third of its value in the first case. In other words, the inductance L was taken as being smaller invalue relative to It, the current remaining the same, in deriving the voltage wave form a.

The entirely similar case where .the current trace is linear but the retrace is exponential as in Fig. 8, is shown in Fig. 11?: and two cases of the resultant voltage wave form required are shown as e and e' for this figure.

Where a very large -value of R is employed in series with L, the voltage applied to cause a saw-tooth current to fiow will necessarily reduce to simply the saw-tooth wave form, while in the other extreme where the series resistance is negligible the voltage wave form necessary to cause a saw-tooth current will reduce to simply impulse wave form. I

Frequently as will be seen in circuits which follow, it is desirable to have capacity in series with the inductance to prevent any direct current fiow through the scanning coils. Such a load circuit and its performance are illustrated in Fig. 11c. For a current of form Fig. 30 to flow in this circuit, the voltage e will be a resultantof Figs. 3b, 3c and 3d, each component being properly adjusted in amplitude to fit the load circuits.

In the case of high (line) frequency scanning the capacity C, of Fig. 110, can generally be made sumciently large so that its reactance is negligible. Hence a parabolic impulse voltage wave form Fig. 3d need not be included as a necessary component of e, and the required vol age wave form reduces to that shown as c. Fig. 111:.

The current through the scanning coils can. of course. be made very large in the type of load circuit of Fig. 110 by having L and C resonant at, or near, the fundamental frequency of the wave form. Such a design. however, materially approximately exponential.

attenuates the harmonic components and generally results in requiring that R be made large. which again reduces thecurrent amplitude as the saw-tooth current wave form is improved.

In the case of low (picture) frequency scanning L is generally so small that its'reactance is negligible. Hence a voltage of impulse wave form, Fig. 31;. need not be included as a necessary component of e. It is, however, almost impossible to make C large enough in this case to pass the fundamental components of the very low frequency wave form, so that its reactance is usually appreciable for picture frequency scanning. When simply a saw-tooth voltage wave form is employed, it will be noted when viewing the scanning pattern on the fluorescent screen, under this condition, that the wave form appears To counteract this effect of exponentiality in the picture trace it is necessary to introduce a compensating wave form, Fig. 3d, of proper amplitude, in combination with the form, Fig. 3c, for low frequency scanning. Thus in Fig. 110 the first. cycle shown is of form Fig. 30, indicated as the wave form of voltage e applied. The current, and hence the voltage ea, Fig. 11c,.is shown as having approximately exponential trace and retrace. The difference in voltage between e and e: is es which is of the which point it opens.

form Fig. 3d (parabolic impulse) as shown of small amplitude in Fig. 111;.

Mathematically, it can be shown that this wave form is composed primarily of the lowfrequency fundamental and the lower harmonics; that is the amplitude ofthe harmonics decreases rapidly with frequency and henoe the observation that discrimination against the low frequency components tends to make the saw-tooth wave form appear exponential is confirmed.

. The simplest arrangement of saw-tooth current generator which satisfies the requirements of Fig. (id is a vibrator or buzzer such as that shown in Fig. 12. Starting with the closing of the contact 0 the voltage across L isconstant except for voltage drop due to resistance in the windings and hence the current rises expopeak which occurs at the "break", as in a "make" and "break" ignition system. The wave-form of voltage, except insofar as it is impaired by sparking at the contacts, will be of the form shown in Fig. 7b and the current as in Fig. 7a. Forgetting for the moment that it is actually the magnetic flux which opens the contact, it is clear that O is a device which is conductive until the current through it reaches a predetermined maximum at Hence the arrangement of Fig. 6d is satisfied by this circuit.

- A vacuum tube may be utilized in two fundamentally different ways to give saw-tooth current through an inductance (this statement being made without regard as to whether or not the voltage control applied to the grid is from a separate source or the result of a feedback). The tube maybe employed as a linear amplifier to repeat the voltage applied to the control grid into the plate circuit as illustrated in our copending application Serial'No. 747,068, filed Oct. 5. 1934. Patent No. 2,052,183, granted August 25, 1936, or

the tube maybe caused to operate as an opening Here vacuum tube 26 has voltage of impulse wave form e applied between its control grid and cathode. In the plate circuit a filter network '(band-pass) comprising elements 21, 28, 29, 30, 8|.32, 38 and the scanning inductance Lia. constitutes. a resistance load for the band of frequencies necessary to simulate the saw-tooth wave form being considered. The voltage e: applied between control grid and cathode is illustrated as being of impulse wave form corresponding to Fig. 327. Hence since the load is resistive (or what is the same thing, the output voltage is a replica of the input voltage) the output voltage across Lin will be of impulse wave form and the current therein will be of saw-tooth form, Fig. 30, according to the derivative series.

Consider now Fig. 13b in which tube 28' is again excited by an impulse wave form eg. Here the load is inductive. C011 34 is assumed to be large compared with the scanning inductanceLsc and capacity 35 is large (low reactance to the scanning frequency) so that Lso is essentially the plate circuit load. If under these conditions tube of its characteristic then the current will not be saw-tooth in form through Lac, with the impulse excitation shown,.since a. voltage drop oc-' current when a large negative bias is employed, is A important. It will be clear under such conditions that tube 26 serves to close the plate circuit during the trace partof the cycle and opens it briefly during the negative impulse peakior the retrace. The current through L under such conditions will be of saw-tooth form. The traces will be exponential approaching linearity to air extent decapacity type circuits for supplying saw-tooth pendent upon the reduction in tube resistance and output circuit resistance.

It was pointed out in Fig. 11 that where sawtooth current is to flow through .;a load of resistance and inductance in series, the applied voltage should bea ,resultant of saw-tooth and impulse components properly proportioned. Likewise in Figs. 6) and 69, it was shown; that the voltage drop across 1, during the trace, which operates against linearity, can be compensated for by a. negative resistance (-r), or an introduced saw-tooth voltage, to compensate for. the

drop across the circuit resistance 1' when sawtooth current flows. Hence coming to Fig. 130 it will be clear that by using a combined impulse and saw-tooth wave form (as there illustrated) for the grid control voltage, current of saw-tooth wave form in the plate circuit can more readily be obtained. Here, in order to avoid a direct current component through the scanning coils a transformer 36, 3'! is employed to couple Lac in the plate circuit as an alternative of the capacity coupled arrangement of Fig. 132:. The effective circuit resistance is represented by resistor 38. If tube 26 is operated as a linear amplifier a fixed value of plate-cathode resistance must be considered in series with resistance 39 and the inductive load. Under such conditions the sawtooth component required will be relatively large and the pollng of voltage e,; is immaterial.

If, however, it is desired to operate tube 28 as ,an opening device, it is important that the impulse peaks be poled to be negative as applied to the grid of tube 26. For such non-linear operation of tube 26 this tube opens the plate circult during the retrace when the grid is highly negative and. during the trace the saw-tooth component acts to compensate for the voltage drop due to tube and circuit resistance thereby holding the voltage across transformer 36, 31 constant and hence assuring good linearity of current traces through Lac.

In our Patent No. 2,052,183 various resistanceand impulse voltage or their combination have been illustrated. One of these forms is here shown in Fig. 14 with the modification that the impulse voltage is directly used to cause sawtooth current to flow through inductance. Thus voltage E charges capacity C substantially linearly with time due to a resistor or constant current device H, such as a suitably arranged space discharge tube, which controls the frequcncygenerated. Tube S acts as the short-circuiting device to discharge 0 when the voltage across C has reached a predetermined value. The action of S is rendered effective by regeneration due to iator source of voltage of passed, so that the voltage across the filter input and output Inc is'of impulse wave form. Therefore, the current (see derivative series Fig. 3),

through I will be of saw-tooth form since the voltage across La, is of impulse wave-form.

Fig. 15 shows a complete circuit for carrying out the. arrangement of Fig. 13b, the impulse wave-form generator being one which has been v illustrated and described in our Patent No.

2,052,183. Voltage source E charges condenser 0 through constant current device, tube H; the value of charging current, and hence thc 'fre-,- quency, being controlled by the grid tap f which sets the bias,on the control grid ofI-I. Short .circuiting tube S, regenerated by the reversing tube Rv acts to short circuit condenser C when its potential has reached a predetermined value which will cause current to'start flowing between plate and cathode of tube S. The current through tube S and hence through its plate rcsistor 40 is of impulse waveform as shown, for examplein Fig. via capacity ll and resistor 42 to the control grid of tube 26. The pollng of this impulse voltage is such that negative peaks are applied to the' grid of tube. The output of tube 26 is similar to that of Fig. 13b and hence theelements are similarly labeled. It will be clear that a current of saw-tooth wave form will flow in scanning inductance Lie. Whether or not the current wave form will be sufilclently linear depends, of course, on the choice of tube 26 and the circuit constants.

8b, and this voltage is applied In Fig. 16 a simplification of Fig. 15 is shown which in practice gives a current of quite good saw-tooth wave form through scanning inductance hi:- Rv fulfills also the function of an output tube.

.Here the feed-back or reversing tube The voltage source E charges capacity C through.

constant current device H, which controls the generated frequency. The shorting of condenser C for the retrace part of'the cycle is accomplished tube S regenerated by tube Rv. Since the,

rrent through tube S is of impulse wave form, the voltage across resistor 40 applied to the grid ortube R is of impulse wave form with the peaks .poled negatively. The output circuit of tube R1) is similar to that of Figs. 13b and 15. The current through L is of saw-tooth form and the voltage across Leo is of impulse form and properly poled so that when applied to the grid of tubes over connection 57 the impulse peaks are positive to regenerate tube S and accelerate the shorting of'capacity C.

In circuits l4, l5 and Hi the points for synchronization and the proper pollng of synchronizing impulses (as from the units l! or 20, Fig.- 2, as the case may be) are indicated by the labels synch. and +synch.". The matter of synchronism is considered at length in our mentioned Patent No. 2,052,183. Tubes with syn: chronizing grids may be employed in the position of S and R2; in these and the following circuits.

The circuits of Figs. 15 and 16, are as noted, arranged to secure either the operation of Fig. 6d or that of Fig. 13b in that a separate generimpulse wave form is provided. The circuit of Fig. 17 is particularly designed to function according to the principles of Fig. 68. Here tube 26 acts as the opening anspvv device when the current in its plate circuit has reached a predetermined maximum. If current of saw-tooth wave form flows in the plate circuit of tube 28, the voltage across resistance 86 will be of saw-tooth form. No current flows between plate and'cathode of tube 8 until a predetermined voltage across resistor 66 is developed. when the voltage across 88 has reached a value sufllcient to cause current to flow in tube 8, a negative voltage is developed at the grid of tube Rv, which tube in turn applies a positive voltage to the grid of 8. Tube 8 is therefore regenerated by tube R1: to cause tube 8 rapidly to short circuit resistor 88. Simultaneously a negative impulse from the plate of tube 8 is' applied to the control grid of tube 28, via the grid blocking condenser 88, and leak resistor 88. Tube 28 thus automatically opens the circuit when the current has reached a predetermined maximum value.

An alternative way of picturing the circuit's operation is to consider tubes 8 and R12 as a source of impulse voltage properly poled and applied to the grid of tube 28, to carry out the requirements of Fig. 13b. The impulse generated is, however, controlled by the rise in current through resistor 68. Resistor 88 is made variable to control the generated frequency. During the trace'part of the cycle when tube 26 is conductive, the time constant is determined by the effective inductance of 38 and resistor 88 plus the remaining circuit resistance. During the retrace the time required for the current to fall depends upon how and increasing resistor 88 serves to increase the operating in accordance with the principles of Figs. 6) and 6g. As in previous figures the scan-,

ning coils Lsc are coupled into the circuit through transformer 88, 87, in part to eliminate the direct current component, and to secure an impedance match for best performance by introducing an effective inductance into the plate circuit of tube 28 to give optimum results. The circuit provides saw-tooth current of quite good wave form, slightly exponential as to traces. It is clear from Fig. 11 and its exposition, that the voltage across coil '86 is of impulse form, that across resistor 68 is of saw-tooth form, and the resultant as applied between grid and cathode of tube Rv via capacity 6| and potentiometer 82 is of combined saw-tooth and impulse wave form.

The tube Rv is a linear voltage amplifier for repeating the combined impulse and saw-tooth voltage in reversed polarity between the grid and cathode of tube 26 via capacity 68 and resistor 88.

The poling of the voltage. wave form of impulseduring the trace part of the cycle it repeats the saw-tooth voltage component so that the grid of tube 26 grows more positive as the trace part of the cycle progresses, i. e., the resistance of the plate-cathode of tube 28 fails to aiford the compensation suggested by the generator eat! of Fig. 8a or the negative resistance (-r) of Fig. 6]. In practice care must be taken with this circuit to avoid overloading the grid of tube Rv.

Instead ofa reversing tube R1) for the feedback as in Fig. 18, a magnetic feedback may be utilized as shown by the addition of a third coil 88, Fig. 19, to the transformer 88, 81. Assumingthe result that current of saw-tooth form flows in coil 38, the voltage across the coil is of impulse wave form and hence, that across coil 84 is likewise of impulse wave form poled to apply the peaks negative to the grid of tube 28. Only the impulse and not the saw-tooth component is appliedback to the grid of tube 28. In practice the frequency is controllable by either an adjustable resistor 88 in the plate circuit, Fig. 19a, or by'resistor 88 in the grid circuit. When one of these resistors is used, the other may be omitted. In either case, an increase of resistance corresponds to an increase of the frequency generated. In practice, a quite acceptable current of sawtooth wave form is obtained through the scanning coils he.

The arrangement of Fig. 19b differs from that of Fig. 19a only in that resistor 61 is employed in the cathode branch common to both plate and grid circuits. Increase of resistor 61 corresponds to increase in generated frequency and in general the performance of the Fig. 1% circuit is slightly superior to that of'Flg. 19a. The circuits of Fig. 19 are moreeifective for high (line) frequency than for low (picture) frequency scanning.

Various other arrangements of the circuits of Figs. 18 and 19 can be made to carry out the principles involved such, for example, as a combination arrangement of the two whereby a reversing tube will serve to perform a part of the feedback and a feedback coupling will serve to perform part of the feedback function.

In our mentioned Patent No. 2,052,183, arrangements were shown for exciting the grid of amplifier circuits with a voltage of combined sawtooth plus impulse wave form. The amplifier circuits there employed were linear and current of saw-tooth wave form through inductance was obtained in the amplifier output circuit by employing considerable resistance in series with the inductance. The generating circuits there shown 0 .grid of the following amplifier tube with the impulse peaks poled negative so that this amplifier tube may function according to the arrangement given and described for Fig. 130. The poling of the wave form is important only when the tube is to operate beyond cut-off" so that the,

current circulates in the loop circuit 68, C and through space path of 8. Hence the voltage drop across resistor 68 applied to the grid of tube Ru causes tube Rv to, in turn, apply a positive impulse peak to the grid of tube S, so that tube Ro acts as the reversing or feedback tube to regenerate tube 8 for rapid discharge oi condenser C. The polarity of the impulse voltage developed across resistor 68 and the saw-tooth voltage developed across condenser C is reversed to that obtainable relative to ground across condenser C, for example, in Fig. 15. It follows then that the combined impulse plus saw-tooth voltage developed across resistor 88 and condenser C is applied to the grid oi. tube 26 through capacity 69 and potentiometer iii, with the poling such that the impulse peaks are negative as applied to the grid of tube 26.

The output circuit of tube 26 could, of course, be of the form shown as the output or plate circuit of Fig. 136 or 13c. In Fig. 20 the output ar-= rangernent comprises resistor ll, capacity l2, scanning inductance Lee and resistor 78. A resistor M in the cathode path gives negative regeneration. This output arrangement is most effective for low (picture) frequencies. The negative regeneration element 73 has been found efiective in maintaining good linearity of the saw-tooth current. trace even when low frequency components areattenuated due to the reactance of capacity 12 (which should be as large a capacity as is feasible) and reaction throughthe power supply elements.

In the output circuit of Fig. 20, as shown (or with a different output as for example, that of either Figs. l3b and 130), currentoi' saw-tooth wave form flows in scanning coils Lac. Where the grid voltage of tube 26 contains an impulse component which is large compared with the saw-tooth component, tube as will operate as an opening device and resistor it may be reduced in value or omitted. Tube 26 can, of course, be operated as a linear amplifier, resistor is being then relatively large. For this condition the saw-tooth component oi the grid voltage would become predominant, and under these conditions the poling of the exciting wave becomes unimportant. The relative magnitudes of the sawtooth and impulse voltage components as applied to the 'grid of tube 26 are determined by the choice of values for resistor 68 and capacity C.

In Fig. 21 the resistance-capacity type of generator employs a voltage source E charging capacity C through constant current tube H. Ca-

pacity C is shorted by tube S regenerated by tube Rv when the voltage across C has reached a predetermined maximum amplitude. This resistance-capacity type of generator is again of the so-called inverted form (as compared with that of Fig. 15 for example) in order that the voltage of combined impulse plus saw-tooth wave form as applied to the grid of tube 26 shall be,

properly poled so that tube 26 may operate as an opening device as described in connection with Fig. 20. Hence the cathode of device H is above ground potential, and in prder that there shall be no relative changes at the generated frequency of voltage between screen grid and cathode, and between the control grid and cathode of tube H, the bias to the control grid, which determines the generated frequency, is furnished by the direct current voltage drop across potentiometer I9 and the direct current potential to the screen grid is through resistor 18. Capacity 11 connects the screen of tube H to its cathode and the time constant of the resistance-capacity branch II, 11 is made to correspond to a frequency lower than the fundamental frequency generated, so that the voltage between screen and cathode remains constant. In a like manner the bias for the control grid tube H maybe secured by connecting its grid througha resistor to a tap on E, and providing a capacity path from control grid to cathode instead of employing 19 as shown. The only adverse criticism to such a connection is that the response 01' the circuit to any change of bias on the control grid for setting the generated frequency is sluggish, due to the time constant 01' the resistor-capacity circuit suggested, which may be made low.

It will be observed that the impulse voltage drop across resistor 78 is applied to the grid of tube Rv poled to make its grid, during the impulse peaks, negative with respect to its cathode, and that tube Rv in turn applies an impulse voltage to the grid of tube S poled to make its grid, during the impulse peaks, positive with respect to its cathode. Tube Ru thus regenerates S to expedite the shorting of condenser C during the retrace part of the cycle. The resultant impulse voltage across resistor 16 and saw-tooth voltage across condenser C are a combined impulse plus saw-tooth voltage properly poled to be applied to the grid of tube 28 through 69 and 7755 so that the action from there on is like that already described for Fig. 20.

, In Fig. 22, another arrangement is shown oi. a resistance-capacity generator inverted to give a properly poled voltage of combined impulse plus saw-tooth wave form applied to the grid of output tube 26. Here voltage source E charges ated by feedback transformer T instead of by a reversing vacuum tube. Resistor 8t (as in Fig. 14) damps the transformer T to prevent spurious oscillation which may occur due to the circuit constants and distributed capacities of T and S. A resultant voltage having an impulse component due to the voltage drop across resistor 15 and a saw-tooth component due tothe voltage drop across condenser C is applied to the control grid of tube 26 through capacity 59 and potentiometer ill. Saw-tooth current flows in output scanning coils Lie as discussed in connection with Fig. 20.

In the three circuits of Figs. 20, 21 and 22, the branch 59, Iii should be of high impedance to prevent its acting as an appreciable load on the generator part of the circuit, and it should provide good fidelity (i. e., a low time constant as determined by capacity 59 and resistor 10) to 'apply the generated voltage wave form undising for the pendulum arrangement 0 there shown, a mechanical interrupter 0 controlled by a vacuum tube oscillator acting as the frequency determining source. With 0 closed the current through winding 36, and hence through scanning coils Lac coupled thereto by winding 31, rises exponentially with time (the exponential approaching linearity as the resistance of the circuit approaches zero). for the trace part of the cycle. The retrace occurs when 0 is briefly opened during each cycle of the frequency generated by tube 80 when the current through polarized windings BI is a maximum. The oscilthrough capacity 82.

lating circuit for tube is of a typical form comprising a tuned grid circuit and feedback winding in the plate circuit. The voltage developed in the plate circuit winding is applied to coil 8i Many variations of the particular arrangement shown willoccur to those skilled in the art. The particular form of the contact 0 may, for example, be of the vacuum tube type to reduce the effects of sparking at the contact.

In Fig. 24, an L/R. type of saw-tooth current generator is shown which employs the negative resistance characteristic of the dynatron to effect its operation. Here tube 88 has a voltage source E applied between cathode and one grid acting as the anode. A direct current bias adjustment, labeled 1, on the grid nearer the cathode serves to determine the slope of the negative resistance characteristic at which operation occurs and also to control the generated frequency. Scanning coil Lsc may be directly introduced in the plate circuit or coupled therein by transformer winding 88, 31 as shown. Resistor 08 represents the resistance introduced by 38, 81, and L which would be made as low as possible. For good wave form of saw-tooth current through Lso the distributed capacities related to winding 38, 31 and Lao should be kept low. The control of frequency by adjustment of the negative bias at I is effective in increasing frequency as the bias is increased. Resistance introduced in the anode (screen) circuit also increases the generated frequency.

The arrangement of Fig. 24 is in practice an economical and efficient generator of current of saw-tooth wave form through the scanning inductances. It is particularly suited to the generation of high (line) frequencies. Synchronization can be achieved by applying the impulses of the synchronizing signal to frequency control grid.

It will be clear to those skilled in the art, that any of the generator units here shown may be substituted and co-ordinated to serve as the units i8 and II of Fig. 2 in a complete receiver and projector of television images.

We claim:

1. In an electric wave generator: a first vacuum tube having grid and plate circuits, means supplying direct current operating potentials to electrodes of said tube, said plate circuit containing inductance and a resistor in series, and means producing in said inductance a current of sawtooth wave form having retrace intervals of short duration relative to the trace intervals, said means comprising, a connection shunting said resistor and containing the space path of a second vacuum tube arranged to pass current when the voltage across said resistor reaches a predetermined value, a capacitive coupling from the grid of the first tube to the plate of the second, and a third vacuum tube regeneratively coupling the input of said second tube to its output, whereby a negative potential is applied to the grid of the first tube from the plate of the second upon occurrence of said predetermined maximum voltage across said resistor thereby to accelerate retrace of said saw-tooth current.

2. In an electric wave generator adapted to provide current of saw-tooth wave form through inductance: a first vacuum tube and a second vacuum tube each having input and output elements, an output load for said first tube comprising inductance and a first resistance in series, means for coupling the output of said first tube to the input of the second tube, means including a second resistance and capacity coupling the output of the second tube to the input of the first tube to provide regenerative feedback in which the frequency determining elements are essentiallysaid inductance and said first resistance whereby the voltage across said inductance is of impulse wave form and the current therein is essentially of saw-tooth wave form, and means for adjusting said first resistance to control the .generated frequency.

said vacuum tube being actuated by current in a said circuits to periodically open said output circult for only a small fraction of each cycle and the winding polarities being such as to provide regeneration between said input and output circuits, a variable resistance included in at least one of said circuits, said resistance and the inductance of said transformer winding in the last said circuit being proportioned to determine the periodicity of the generated wave, means for adjusting said resistance to control said periodicity and means for coupling said third winding to the scanning inductance.

4. In an electric wave generator adapted to provide a current of saw-tooth wave form through a scanning inductance, a circuit effectively including said scanning inductance and comprising. in series, inductance means, resistance means, a normally fully conductive circuit controlling device, and a source of operating voltage for said circuit, means responsive to operating conditions in said circuit for periodically rendering said device substantially completely nonconductive for only a small fraction of each cycle and means for adjusting said resistance means to control the periodicity of said generator.

5. In an electric wave generator adapted to provide a current of saw-tooth wave form through a scanning inductance. a circuit effectively including said scanning inductance and comprising, in series, inductance means, resistance means, a normally fully conductive circuit controlling device comprising the space-current path of a vacuum tube, and a source of operating voltage for said circuit, means responsive to a predetermined current through said circuit for periodically rendering said device substantially completely non-conductive for only a small fraction of each cycle and means for adjusting said resistance means to control the periodicity of said generator.

6. In an electric wave generator adapted to provide a current of saw-tooth wave form through a scanning inductance, a circuit effectively including said scanning inductance and comprising, in series, inductance means, resistance means, anormally fully conductive circuit controlling device including the space-current path of a vacuum tube, and a source of operating voltage for said circuit, means responsive to operating conditions in said circuit for periodically rendering said device substantially completely non-conductive for only a small fraction of each cycle and means for adjusting said resistance means to control the periodicity of said generator.

7. In an electric wave generator adapted to provide a current of saw-tooth wave form through a scanning inductance, a circuit effectively including said scanning inductance and comprising,

in series, inductance means, resistance means, a normally fully conductive circuit controlling device including the space-current path of a vacuum tube, and a source of operating voltage for said circuit, vacuum tube means responsive to operating conditions in said circuit for periodically rendering said device substantially completely non-conductive for only a small fraction. 01 each cycle and means for adjusting said resistance means to control theperiodicity of said generator.

8. In an electric wave generator adapted to provide a current 0! saw-tooth wave form through a scanning inductance, a circuit efiectiveiy in eluding said scanning inductance and comprising, in series, inductance means, resistance means, a normally fully conductive circuit controlling device, and a source of operating voltage for said 

